1. Field of the Invention
The present invention relates to an eddy current testing apparatus, an eddy current testing probe, and an eddy current testing method, which are suitable to inspect a defect on an inner wall surface of a groove-shaped portion (slot) having a large depth and the same cross-sectional shape in a depth direction.
2. Description of the Related Art
There is an eddy current testing method as a method for detecting a surface defect of an object to be inspected. In the eddy current testing method, an alternating magnetic field that is generated by a coil current is applied to the conductive object to be inspected, and disturbance of an eddy current that is induced in the object at that time is detected by a change in coil impedance, thereby evaluating whether or not a defect is present in the object to be inspected.
In recent years, eddy current testing is frequently used as a method for detecting a defect on or in an inner wall surface of a groove-shaped portion such as a blade fitting portion (also called dovetail) of a turbine disk or a slot of a rotating unit such as a generator. For example, Japanese Patent No. 4130539 discloses an example of an eddy current testing probe configured by embedding a coil in a member that conforms to a cross-sectional shape of a groove-shaped portion such as a dovetail, while the cross-sectional shape of the groove-shaped member does not change in its depth direction (length direction) or the groove-shaped member has the same cross-sectional shape in its depth direction. In addition, Japanese Patent No. 4464096 discloses an example of an eddy current testing probe configured by forming a coil-shaped wiring on a flexible printed board. The flexible printed board can be placed in contact with an inner wall surface of a groove-shaped member while conforming to a cross-sectional shape of the groove-shaped member.